Dietary chromium-methionine improves feed conversion and alters plasma triglycerides in broilers under cyclic heat stress

The objective of this study was to evaluate the effects of chromium-methionine (CrMet) supplementation in broiler diets under cyclic heat stress. A total of 1,000 one-day-old male Cobb 500 broilers were assigned to a completely randomized design with five dietary treatments (0, 0.25, 0.50, 1.0, and 2.0 mg CrMet/kg) and 10 replicates of 20 birds each. Broilers were reared under thermoneutral temperatures until 21 days and exposed to cyclic heat stress from 22 to 42 days. Broilers fed 2.0 mg showed lower feed conversion ratio (FCR) than those receiving 0.50 and 1.0 mg and the control from 21 days, with 0.75 mg estimated as the optimal level. From to 42 days, broilers fed 1.0 mg exhibited lower FCR than those receiving 0.25, 0.50 mg and the control, with an estimated optimum of 0.88 mg. Cloacal temperature was not affected, whereas supplementation with 0.25 mg was associated with lower mortality. At 42 days, plasma triglyceride levels were reduced in broilers supplemented with 1.0 and 2.0 mg compared with those receiving 0.25 mg and the control, showing a linear response. Thyroxine levels were lower in the 0.25 mg treatment compared with the 2.0 mg and control treatments, while gene expression of IGF-1 and GHR was not affected. In conclusion, CrMet improved feed efficiency under heat stress, with optimal inclusion levels of 0.75 and 0.88 mg/kg from 21 and 42 days, respectively, while 0.25 mg reduced mortality and higher levels reduced plasma triglycerides.